Heat exchanger

ABSTRACT

A surface polyaniline layer comprising a polyaniline and/or a derivative thereof capable of generating active oxygen or hydrogen peroxide upon the reaction with the water component in external air that comes in contact therewith, is formed on at least a portion of the outermost surface of a base body constituting tubes and/or fins, wherein a benzenoid/quinoid ratio in the surface polyaniline layer (defined as a ratio of an absorbancy of the benzenoid structure to an absorbancy of the quinoid structure in the polyaniline and/or the derivative thereof) is in a range of about 0.5 to about 3.0.

TECHNICAL FIELD

The present invention relates to a heat exchanger. More specifically,the invention relates to a novel heat exchanger having tubes equippedwith heat-exchanging members, of an air conditioner such as a vehicleair conditioner and the like, with resistance to water and chemicals, aswell as functions for decomposing and deodorizing malodorous substancesand sterilizing harmful microorganisms adhered to heat-exchangingmembers, such as fins and plates and surfaces of the tubes. According tothe heat exchanger of the present invention, a polyaniline is used onthe surfaces of the heat-exchanging members, such as tubes, fins, platesand the like to efficiently generate hydrogen peroxide and active oxygenthat remove orders or to effect sterilization.

BACKGROUND ART

It has been known that hydrogen peroxide generates active oxygen, suchas —OH due to its own effect or by bringing it into contact with ironions. As its effect can be reliably expected along with chlorine, ozone,ultraviolet rays, a photo catalyst and the like, hydrogen peroxide hasbeen used for sterilization or disinfection in a variety of fields.

As a method of generating hydrogen peroxide, it has been known to bringpolyaniline into contact therewith. For example, Japanese UnexaminedPatent Publication No. 9-175801 (JP-A-9-175801) discloses an activeoxygen-generating agent containing a polyaniline capable of generatingactive oxygen useful for sterilizing microorganisms living in water, anda method of generating active oxygen by using the same. JP-A-10-99863discloses a method of utilizing a superoxide for sterilization, which isgenerated by arranging in a city's water supply an anode and a cathodehaving polyaniline on the surface thereof, and causing a current to flowbetween the two electrodes, to sterilize water such as drinking waterand cooling water, and a water treating apparatus used for the method ofsterilization. JP-A-10-316403 discloses generating superoxide anionradicals by coating the surface of an electrically conductive substancewith an electrically conductive composition composed of a powder of anelectrically conductive material and/or fibers, a binder and apolyaniline, and causing a current to flow using the coating as acathode to generate active oxygen in water.

Further, an apparatus for generating active oxygen is disclosed inJP-A-11-79708. The apparatus for generating active oxygen ischaracterized by including an anode and a cathode supporting a redoxpolymer, such as polyaniline or a derivative thereof which has theability to generate active oxygen, and having between the two electrodesa spacer of a thickness in a range of 0.005 to 5 mm which isliquid-permeable or liquid-penetrating. JP-A-11-158675 discloses anapparatus for generating active oxygen which is characterized by havingan electrode and particles on the surfaces thereof a redox polymer, suchas polyaniline or a derivative thereof which has the ability to generateactive oxygen.

In addition, JP-A-8-500700 discloses a method of producing a metallicmaterial protected from corrosion and a material obtained by the method.More specifically, JP-A-8-500700 teaches a method of producing ametallic material, comprising the steps of (a) forming a layer of anintrinsically conductive polymer capable of absorbing water, preferablya polyaniline, in a non-electrochemical manner on a metallic material,such as a metallic material treated with phosphate, a metallic materialsuch as a steel, stainless steel, copper, aluminum, bronze or any otheralloy that has corroded, (b) contacting the metallic material coatedaccording to step (a) with a passivating medium comprisingoxygen-containing water for a period of at least 30 seconds, (c) asrequired, conducting a secondary passivation treatment, (d) as required,removing the layer of the electrically conductive polymer, and (e)providing the metallic material with a corrosion-protection covering.The ultimate object of the invention is to attain protection from thecorrosion by forming a passivation film on the surface of the metallicmaterial. The layer of the water-absorbing polymer, or preferably, apolyaniline formed according to step (a) can be also removed accordingto step (d).

SUMMARY OF INVENTIONS

An object of the present invention is to provide a novel heat exchangerhaving tubes and fins like an air conditioner such as a vehicle airconditioner, which guarantees durability, and has functions fordecomposing and deodorizing malodorous substances deposited on thesurfaces of the tubes and fins, sterilizing harmful microorganisms, aswell as maintaining fundamental performance without decreasing thedecomposing and deodorizing, and sterilizing functions.

The inventors of the present invention noted that the above-describedpolyaniline is capable of generating hydrogen peroxide when moisture orother water component has come in contact therewith, and have conductedextensive studies in an attempt to develop a method of efficientlymaintaining the capability of the polyaniline for generating hydrogenperoxide for extended periods of time, and an apparatus that utilizesthe above method. As a result, the inventors have discovered that, aftera large amount of active oxygen stemming from hydrogen peroxide has beengenerated from the polyaniline, the ability to generate active oxygen,and then conceived of the present invention based on the abovediscovery.

The present invention is intended to enhance the ability to generateactive oxygen by selecting the structure of the polyaniline that easilygenerates active oxygen. Generally, it is considered that polyanilinehas a high capability to generate active oxygen when a benzenoidstructure and a quinoid structure are present at a ratio of 1:1 in thepolyaniline molecules. However, it has been discovered that when anelectric current is caused to flow using the polyaniline as the cathodeat an accelerated test, the ratio of the quinoid structure increases,and the ability to generate active oxygen decreases. In order topermanently generate active oxygen, the ratio of the benzenoid structureto the quinoid structure must be controlled. The ratio is ideally 1:1,but active oxygen can be sufficiently generated at a ratio of 1:2.Therefore, in order to permanently generate active oxygen from thepolyaniline, the present invention provides a method of generatingactive oxygen wherein the structure of the polyaniline is controlledrelying upon the absorbancy ratio thereof when the film is being formedor when deterioration of the film is discovered, and a heat exchangerhaving a function for generating active oxygen.

The present invention is concerned with a heat exchanger equipped withat least one tube having at least one fin, wherein:

at least one tube and/or at least one fin are composed of at least abase body and a surface film formed on at least a portion of anuppermost surface of the base body,

the surface film is a surface polyaniline layer composed of apolyaniline and/or a derivative thereof capable of generating activeoxygen or hydrogen peroxide by reacting with a water component inexternal air that comes in contact therewith, and

a ratio of benzenoid to quinoid in the surface polyaniline layer is in arange of about 0.5 to about 3.0, which is defined as a ratio of anabsorbancy of a benzenoid structure to an absorbancy of a quinoidstructure in the polyaniline and/or in the derivative thereof.

In another aspect, the heat exchanger of the present invention furthercomprises a means for bringing the benzenoid/quinoid ratio back into apreset range of about 0.5 to about 3.0, when the benzenoid/quinoid ratiohas fallen outside the preset range in the surface polyaniline layer.The means for bringing the benzenoid/quinoid ratio back is preferably astructure-converting means for converting the benzenoid structureconstituting the polyaniline and/or the derivative thereof into thequinoid structure, or for converting the quinoid structure into thebenzenoid structure.

As a result of employing the above-mentioned constitution for the heatexchanger of the invention, the malodorous components or bacteria aredecomposed or sterilized at a normal temperature due to the oxidizingaction of active oxygen generated by the polyaniline and/or thederivative thereof which has been firmly coated on the heat exchangerhaving large contact areas. It is, therefore, possible to preventmalodorous components or bacteria from becoming a generating source ofmalodor or a source of bacteria for extended periods of time withouthindering water-wetting performance of the heat exchanger.

According to the heat exchanger including tubes having heat-exchangingmembers such as fins and plates of the present invention, as understoodfrom the following detailed description, not only durability can beobtained, such as resistance to water and chemicals, but also thestructural ratio of benzenoid to quinoid can be maintained in thesurface polyaniline layer to suppress adhered malodors and to maintainfundamental performance of the heat exchanger, without lowering theability to generate active oxygen of the polyaniline, after the film hasbeen formed or has been used. Therefore, the present invention can beadvantageously utilized for a vehicle air conditioner mounted to avehicle, air conditioner, radiator and any other heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view schematically illustrating an evaporatorfor a car using a heat exchanger according to the present invention.

FIG. 2 shows a partial sectional view illustrating a preferredembodiment of a heat exchanger of the present invention.

FIG. 3 shows a partially enlarged sectional view illustrating a portionof a fin of the heat exchanger shown in FIG. 2.

FIG. 4 shows a partially enlarged sectional view illustrating anotherpreferred embodiment of a fin of a heat exchanger of the presentinvention.

FIG. 5 shows a partially enlarged sectional view illustrating a furtherpreferred embodiment of a fin of a heat exchanger of the presentinvention.

FIG. 6 shows partially enlarged sectional view illustrating a stillfurther preferred embodiment of a fin of a heat exchanger of the presentinvention.

FIG. 7 shows a partially enlarged sectional view illustrating yetfurther preferred embodiment of a fin of a heat exchanger of the presentinvention.

FIG. 8 shows a graph plotting a relationship between a benzenoid/quinoidratio and a concentration of generated hydrogen peroxide in a surfacepolyaniline layer of the present invention.

FIG. 9 shows a graph illustrating changes in a benzenoid structure andin a quinoid structure as changes in absorbency thereof when an electricpotential is applied to a polyaniline.

FIG. 10 shows a chemical formula representing a change from a quinoidstructure to a benzenoid structure when an electric potential is appliedto the polyaniline.

FIG. 11 shows a graph illustrating a change in a benzenoid structure andin a quinoid structure as a change in an absorbancy when an oppositeelectric potential is applied to a polyaniline.

FIG. 12 shows a chemical formula representing a change from a benzenoidstructure to a quinoid structure of when an opposite electric potentialis applied to a polyaniline.

FIG. 13 shows a graph plotting changes in a benzenoid/quinoid ratio andin an active oxygen generating capability when an electric potential andan opposite electric potential are successively applied to apolyaniline.

DETAILED DESCRIPTION

The present invention relates to a heat exchanger, and particularly, aheat exchanger of an oxygen peroxide-generating type, and can beadvantageously put into practice in various forms. The heat exchanger ofthe present invention is not limited to the forms that are describedbelow.

The heat exchanger of the invention is equipped with tubes which have atleast one heat-exchanging member, such as a fin(s) (vanes), a plate(s),etc. (hereinafter referred to as “a fin(s)”), and forms thereof canencompass various forms. In other words, the heat-exchanging membersused for improving the heat-exchanging efficiency of the heat exchangerinclude various forms such as fins, plates, etc., and are desirablyconfigured with members having large surface areas. As described laterconcerning the base body, the heat-exchanging members are preferablyconfigured with a light metallic material. The size of the fin can bearbitrarily varied depending upon the desired effect.

The tubes having fins can also encompass various forms. For example, thetubes may have a circular shape, a rectangular shape or a flat shape,such as a crushed circular shape, in cross section. To modify the heatexchanger to be small and light weight, it is desirable that the tubeshave a flat shape in cross section, and the tubes be made of a lightmetallic material in the same manner as fins. The size of the tube canbe arbitrarily varied depending upon the desired effect in the samemanner as fins, as a matter of course.

The tube with at least one fin can be variously arranged in the heatexchanger, and there is no particular limitation on the arrangement andthe structure thereof. For example, a long tube with a plurality of finsmay be folded a plurality of times to constitute a heat exchanger havinga predetermined shape, or a tube member composed of a plurality of tubesand a plurality of fin members in a shape being adapted to the tubemember, and the tube member and fin members joined together toconstitute the heat exchanger.

Typical examples of the heat exchanger include an evaporator and acondenser used for an air conditioner for a vehicle, i.e., a car airconditioner. In addition to the car air conditioner, examples of theheat exchanger include an air conditioner, radiator and the like,without limitation thereto.

FIG. 1 schematically illustrates a use of the heat exchanger in a carair conditioner, i.e. use as an evaporator. Slightly hot air (indicatedby arrow A) is sent from a blower 21 to a car air conditioner 22. Thehot air further passes through a filter 23 and arrives at a heatexchanger 10 where heat is exchanged. The air (cold air) cooled throughthe exchange of heat is exhausted in a direction indicated by arrow Bthrough a duct 24 attached to the car air conditioner 22.

As described above, the heat exchanger 10 can have various forms. FIG. 2is a sectional view schematically illustrating a potion of the heatexchanger 10. The heat exchanger 10 is obtained by joining fin members17 to a tube member 15. A surface polyaniline layer 2 is provided on allof the uppermost surfaces of both members that are joined together. Ifnecessary, the surface polyaniline layer 2 may be partially omitted. Thetube member 15 has a base body 1 made of an aluminum alloy of which theexposed portions are covered with the surface polyaniline layer 2. Acoolant 16 flows inside the tube member 15. The coolant 16 is, forexample, a fluorine-containing hydrocarbon-based coolant such as1,1,1,2-tetrafluoroethane (hydrofluorocarbon (HFC) such as HFC 134a).Herein, fin members 17 having a rugged pattern in cross section in orderto increase heat-exchange efficiency are attached by brazing (not shown)onto one side of the surface of the tube member 15. Like the tube member15, each of the fin members 17 has a base body 1 made of an aluminumalloy, the exposed portions of which are covered with the surfacepolyaniline layer 2. The drawing show the fin members 17 having a ruggedshape in cross section. It is, however, also possible to use fin members17 having a recurring triangular sectional pattern like bellows or finmembers 17 having any other sectional pattern instead of a ruggedcross-section pattern.

Concretely, FIG. 3 is a sectional view illustrating the fin portion inthe heat exchanger shown in FIG. 2 by further enlarging it. In the heatexchanger of this invention as shown, the fin 17 consists of a base body1 and the surface polyaniline layer 2 formed on the uppermost surfacethereof. Although no other layers are shown in FIG. 3, an interlayeredintermediate layer may be provided, or any other layer may be providedbetween the base body 1 and the surface polyaniline layer 2, asdescribed below. Further, the base body 1 and the surface polyanilinelayer 2 may be subjected to any treatment in order to improve thejunction therebetween. Further, the surface polyaniline layer 2 may beadditionally subjected to arbitrary treatment on its surface.

On the fins and the tube provided therewith, the base body can be formedby using various materials. However, a metallic material, and aparticularly light metal, such as a metallic material containingaluminum (aluminum alloy or aluminum mixture) can be advantageouslyused. This is because, the aluminum-containing metallic material islight in weight, efficiently exchanges heat and has excellent durabilityand corrosion resistance. Typical aluminum-containing metals are Al—Mnalloys and the like. As a material useful for constituting the basebody, other than the aluminum-containing metal, there can be exemplifiedcopper and a resin material.

The fins and the tubes provided therewith can be advantageously formedby molding the aluminum-containing metallic material or any othermetallic material which is the base body material. As a suitable methodof molding, there can be exemplified extrusion molding and pressworking. If necessary, these members may be produced by, for example,forging or cutting instead of molding.

The fins and the tubes may be produced separately or may be integratedtogether through a subsequent step. The fins and tubes may also besimultaneously or nearly simultaneously formed integrally together.Generally, it is desirable that the fins and the tubes are formed bymolding using the same metallic material. Any junction means can be usedwhen the fins and the tubes are to be integrally formed together througha subsequent step like in the former method. As a suitable junctionmeans, brazing can be exemplified. When brazing is used, the brazingagent is washed and removed with an acid or an alkali after the junctionhas been completed.

The surface polyaniline layer may be provided on the entire uppermostsurface of the base body that constitutes fins and tubes or may bepartially provided on the uppermost surface of the base body. Asrequired, the surface polyaniline layer may be provided on the entireuppermost surfaces of the fins or tubes only or may be selectivelyprovided on only portions of the uppermost surfaces of the fins or thetubes. FIG. 2 illustrates an embodiment in which the surface polyanilinelayer 2 is provided on the entire uppermost surfaces (uppermost surfacesof the base body 1) that are the exposed tube member 15 and the finmembers 17 of the heat exchanger 10.

It is desirable that the surface polyaniline layer is formed on theentire uppermost surfaces of the base body 1, but may be selectivelyformed on the required portions as required. The surface polyanilinelayer can be formed by using a polyaniline having a benzenoid structureand a quinoid structure as represented by the following general formulaand/or a derivative thereof. The compound which is hereinafter simplyreferred to as “polyaniline-based compound” undergoes reaction with awater component in external air that is brought into contact therewithand generates hydrogen peroxide or active oxygen. The “water component”referred to here includes moisture, water and any other form of watercontained in external air or in an external atmosphere.

The polyaniline-based compound represented by the above formula iscommercially available from Aldrich Co., under the trade name“Polyaniline Emeraldine Base”. As derivatives of polyaniline, though notlimited thereto, there can be exemplified sulfonated polyaniline and thelike.

In the heat exchanger of the present invention, the ratio of thebenzenoid structure to the quinoid structure in the surface polyanilinelayer plays an important role. The ratio of the two structures, i.e. thebenzenoid/quinoid ratio can be defined as a ratio of an absorbancy ofthe benzenoid structure to an absorbancy of the quinoid structure in thepolyaniline and/or in the derivative thereof, and is preferably in arange of about 0.5 to about 3.0 and, more preferably, in a range ofabout 1.0 to about 2.0. The absorbancy can be measured by using, forexample, an absorbancy meter “UV-2500PC” (trade name) manufactured byShimazu Mfg. Co. or “U-4100” (trade name) manufactured by Hitachi HighTechologies Co.

The surface polyaniline layer can be formed in various thicknesses, fromabout 0.1 to about 10 μm, preferably from about 0.1 to 1 μm, and morepreferably from about 0.1 to about 0.5 μm. If the thickness of thesurface polyaniline layer is less than 0.1 μm, the desired action andeffect cannot be expected. If the thickness thereof exceeds 10 μm, onthe other hand, there is a problem that it becomes difficult to form afilm.

Various compositions and film-forming methods can be used for formingthe surface polyaniline layer. For example, the surface polyanilinelayer can be advantageously formed by using a solution, such as apolyaniline-containing solution which is preferred for forming thesurface polyaniline layer, and has for example, the followingcomposition:

Polyaniline about 1 to about 5% by wt. Binder (carbodiimide about 1 toabout 20% by wt. compound) Solvent (water) about 80 to about 98% by wt.

The above composition can be arbitrarily varied, as a matter of course.As a binder, for example, a polymer, a silane coupling agent and thelike which have a sulfuric acid group or a phosphoric acid group can beadvantageously used. As the solvent, alcohols such as methanol orethanol can be used instead of water in nearly the same amount as water.

Various film-forming methods can be used for forming the surfacepolyaniline layer. Advantageously, however, there is usually a dippingmethod used for dipping a precursor of the heat exchanger in thepolyaniline-containing solution, or an application method for applyingthe polyaniline-containing solution. For example, the dipping method canbe advantageously carried out by dipping the precursor of the heatexchanger in the polyaniline-containing solution at a temperature ofabout 4 to about 30° C. for about one minute.

In the heat exchanger of the present invention, the surface polyanilinelayer constituting the uppermost layer can be improved in a variety ofways.

For example, in the fin 17 for the heat exchanger shown in FIG. 4, thesurface polyaniline layer 2 formed on the base body 1 may further havehydrophilic functional groups (abbreviated here as FG) on the surfaceportion thereof. The hydrophilic functional groups FG may be variousfunctional groups having hydrophilic property, and are preferablyselected from a primary amino group, a secondary amino group, a tertiaryamino group, an ammonium group, a nitric acid group, a carboxyl group, asulfonic acid group and hydroxyl group. One kind of these functionalgroups may be solely introduced or two or more kinds of these functionalgroups may be introduced in combination. The presence of the hydrophilicfunctional groups FG is useful particularly for improving thewater-wetting property of the heat exchanger.

The hydrophilic functional group described above can be preferablyintroduced into a binder used for the polyaniline compound duringforming the surface polyaniline layer from the polyaniline compound.More preferably, the hydrophilic functional group may be introduced inadvance into the binder. Desired binders may include a carbodiimidegroup, a carboxyl group and the like, but are not limited thereto. Forexample, due to the work of the binder, the hydrophilic functionalgroups can be easily added to amino groups in the polyaniline-basedcompounds, and can be uniformly distributed over the surface of theformed surface polyaniline layer.

The fins and tubes are usually formed by using the base body that isreferred to in the present invention. The base body for these members isformed by molding any metallic material, such the light metallicmaterial as described earlier, however the fins and tubes may be made ofthe same metallic material or different metallic materials.

As the metallic material, there can be exemplified a metallic materialcontaining aluminum, i.e. an aluminum-containing metallic material.Herein, the aluminum-containing metallic material is generally analuminum alloy containing aluminum at an arbitrarily given ratio,however, the aluminum-containing metal may be a metallic materialcontaining aluminum in any other form. A typical aluminum-containingmetal is an Al—Mn based alloy as described above.

The fins and tubes are usually formed from a single layered or a singlemetallic material. As required, they may consist of a composite body ofat least two metallic material layers. In the metal composite body, itis desirable that the amount of the metallic material having a higheroxidation-reduction potential is increasing from the upper metallicmaterial layer toward the lower metallic material layer. This isbecause, upon introducing an inclined oxidation-reduction potential intothe metallic material that constitutes the base body, it is possible toprevent the occurrence of undesired oxidation of the base body while theheat exchanger is being used. When the metal composite body of athree-layered structure is employed, the third metallic material layerarranged in contact with the surface polyaniline layer is allowed tohave any oxidation-reduction potential in a range from the highest valueor a value lower than it, and to a value higher than the lowest value,compared to the oxidation-reduction potentials of the first and secondmetallic material layers under the third metallic material layer.

FIG. 5 is an example in which the base body 1 for the fin 17 has beenconstituted by a composite body of two metallic material layers. Asshown there, the base body 1 is constituted by a lower metallic materiallayer 11 and an upper metallic material layer 12. This is an example ofthe base body 1 for the fin 17. However, this is not limited to thisexample only, the same also holds for the other fins 17. Similarly, thebase body for the tube may also be constituted by the lower metallicmaterial layer 11 and the upper metallic material layer 12.

In the metallic material composite body shown in FIG. 5, the lowermetallic material layer preferably consists of an aluminum (Al) alloyand the upper metallic material layer preferably consists of a zinc(Zn)-containing metallic material. Further, the lower metallic materiallayer preferably consists of an Al—Mn alloy, and the upper metallicmaterial layer preferably consists of a metallic material which containssilicon (Si) in addition to zinc. In particular, the upper metallicmaterial layer preferably consists of an aluminum alloy, which containsaluminum (Al) and negligible amounts of impurities in addition to zincand silicon.

As schematically illustrated in FIG. 6, the surface polyaniline layer 2may further contain a dopant 18 dispersed therein. When used in thepresent invention, the dopant exhibits a bonding action for bonding thepolyaniline to the underlying base body and can, therefore be referredto as a “binder”. Preferably, the dopant is deposited on the polyanilineand/or the derivative thereof due to the electrostatic interaction. Ifdescribed with reference to the general formula of the polyanilinedescribed above, the dopant generally deposits on a nitrogen atom of an—NH— group among the adjacent benzene rings or on a nitrogen atombetween the benzene ring and the polyaniline ring adjacent each other.

When the surface polyaniline layer is provided according to the presentinvention, an interlayered intermediate layer may be further providedbetween the surface polyaniline layer and the underlying base body. FIG.7 is a partially enlarged sectional view illustrating the above heatexchanger, wherein, as shown, the fin 17 further has an interlayeredintermediate layer 3 between the surface polyaniline layer 2 and theunderlying base body 1. The interlayered intermediate layer usuallyworks to enhance the adhering force of the surface polyaniline layer tothe base body, and prevent electrons from being robbed by thepolyaniline (prevention of rust).

The interlayered intermediate layer can be formed by using variousmaterials, and preferably, comprises a non-metallic material. Preferredexamples of the interlayered intermediate layer include an insulatingfilm, an antioxidizing film, a nonmetallic material having anoxidation-reduction potential which is higher than in the polyanilinecompound, and the like. More concretely, for example, a chromate film ora polyamide film can be used. The interlayered intermediate layer isusually a single layer. However, as required, two or more interlayeredintermediate layers may be used in combination. There is no particularlimitation of the thickness of the interlayered intermediate layer.

In the present invention as already described above, the ratio of thebenzenoid structure to the quinoid structure in the surface polyanilinelayer, i.e. the benzenoid/quinoid ratio, is usually in a range of about0.5 to about 3.0 and, more preferably, in a range of about 1.0 to about2.0. This is because, as shown in FIG. 8, if the benzenoid/quinoid ratiobecomes less than 0.5, the concentration of the generated hydrogenperoxide, in other words, the capability of generating the active oxygendecreases. In a portion that is hatched in FIG. 8, as a more importantmatter, a malfunction such as peeling of the surface polyaniline layerfrom the base body or dissolution of the surface polyaniline layeroccurs in a subsequent step. Further, if the benzenoid/quinoid ratioexceeds 3.0, the concentration of the generated hydrogen peroxidesharply decreases at a nearly constant rate.

Thus, in the present invention, it is important to maintain thebenzenoid/quinoid ratio constant in the range of about 0.5 to about 3.0.In other words, in case the benzenoid/quinoid ratio in the surfacepolyaniline layer deviates from the range of 0.5 to 3.0, the means forbringing the benzenoid/quinoid ratio back in the preset range can befurther provided. In the case of the present invention, this means isone for converting the benzenoid structure constituting the polyanilinecompound into the quinoid structure, or one for converting the quinoidstructure into the benzenoid structure, and therefore, can be referredto as “structure conversion means”.

Here, the benzenoid/quinoid ratio and the structure conversion means forits adjustment will be described in further detail.

FIG. 9 shows a change in the structure of the polyaniline due to theapplication of a voltage, which was observed as a change in theabsorbancy from the absorbancy spectra, the benzenoid structure in thepolyaniline can be detected near the wavelength of about 350 nm, and thequinoid structure can be detected near the wavelength of about 650 nm.Further, the benzenoid/quinoid ratio can be easily calculated from theratio of the absorbancies.

When voltage is applied, on the other hand, the benzenoid structure(i.e. absorbancy thereof) increases while the quinoid structure (i.e.absorbancy thereof) decreases, in the polyaniline. In the presentinvention, the anode of the sample was connected to a power source (+),the sample was dipped in 50 ml of pure water, and thereafter, a voltageof 2 volts was applied for different periods of time period (0 hour, 24hours and 96 hours) by stirring with a stirrer. The eluates weremeasured for their absorbancy spectra for their respective time periods,and the results were plotted as shown in FIG. 9. From these results, itwas presumed that a change in the structure occurred in the polyanilineas shown in FIG. 10.

Even when the structure has changed in the polyaniline as describedabove, the quinoid structure can increase and the active oxygengenerating capability can be restored in the present invention, byapplying a potential opposite to the voltage applied to the same sample,i.e. by applying an opposite potential. However, if the oppositepotential is applied for extended periods of time, the quinoid structureincreases to a degree more than expected and other portions areoxidized, causing the polyaniline to become soluble in water, and mayelute out into water from the electrode plate. Thus, it is desirablethat the opposite potential is correctly applied for a short period oftime. The time for applying the opposite potential is usually withinabout 2 hours, preferably within about one hour, and more preferably ina range of about 30 minutes to about 60 minutes.

FIG. 11 shows a plot of results obtained by measuring the absorbancyspectra of the eluates according to the same manner as described in FIG.10, but changing into the opposite potential. In other words, in thiscase, the electrode connected to the power source (+) was changed fromthe anode into the cathode, the sample was dipped in 50 ml of purewater, and then a voltage of 2 volts was applied for different periodsof time (0 minute, 30 minutes and 60 minutes) by stirring with astirrer. The eluates were measured for their absorbancy spectra fortheir respective time periods, and the results were plotted as shown inFIG. 11. From these results, it was presumed that a change in thestructure occurred in the polyaniline as shown in FIG. 12.

Further, based on the measured results of FIGS. 9 and 11, thebenzenoid/quinoid ratios and the active oxygen generating capabilities(ppm) were plotted as a function of time, and to obtain a graph as shownin FIG. 13. As understood from this graph, the benzenoid/quinoid ratiocan be restored to the initial state by applying the opposite potentialfor only a short period of time. Accompanying this restoration, theactive oxygen generating ability can also be restored near the initialstate.

The above results cannot be achieved, if the surface polyaniline filmhas fine defects such as pinholes or has not been perfectly formed. Ifthe solution used in the subsequent steps directly infiltrates into thebase body of the heat exchanger, the surface polyaniline film may peeloff or its properties may be deteriorated. Therefore, a film evaluationstep is necessary for evaluating whether, after formed, the surfacepolyaniline film has defects or has not been perfectly formed. Afterthis step, the surface polyaniline film can be removed if it has defectsor has not been perfectly formed. As a method of detecting pinholes, forexample, a predetermined measuring point is observed by using an opticalmicroscope, the image is taken in as electronic data, turned into abinary form (white: aluminum substrate and pinholes, black: polyaniline)by using an image processing software, and the white portions aredetected to easily discover the pinholes in a short period of time. Intimes other than during production, a metal having anoxidation-reduction potential higher than the chromate or thepolyaniline is formed as an underlying film, and thereafter, thepolyaniline film is formed to prevent pitting caused by the occurrenceof pinholes, i.e. to decrease the problem of corrosion.

For instance, when a water-absorbing polymer film or preferably, a thinpolyaniline film is formed on the surface of a metallic material such asaluminum, iron or zinc according to a method disclosed in JP-A-8-500700referred to earlier, there is no problem if the film is perfect.However, if the polyaniline film is partially damaged and the underlyingpassivated metallic material is exposed, electrons are robbed from themetallic material of the exposed region, and corrosion occurs in aconcentrated manner from the exposed portion. If corrosion occurs in thetubes of the heat exchanger, coolant may leak or scatter throughopenings (pinholes) in the corroded portion decreasing the function ofthe heat exchanger.

As described above, the structure conversion means advantageously actsto adjust the benzenoid/quinoid ratio and the active oxygen generatingcapability. The structure conversion means can assume variousconstitutions, but is desirably, the voltage applying means as describedabove. For instance, an opposite electrode composed of another basemember is arranged for the heat exchanger, and current is caused to flowby the voltage applying means across the heat exchanger and the oppositeelectrode to rob electrons from the surface polyaniline layer, therebyachieve the desired object.

According to another preferred embodiment, the structure conversionmeans may be a voltage applying means with means for switching thecurrent-flowing direction. By using this structure conversion means, incase the benzenoid/quinoid ratio has exceeded the preset range of 0.5 to3.0, the current can be flowed in the opposite direction across the heatexchanger and the opposite electrode.

It is further desirable that the structure conversion means is equippedwith a timer means. Use of the timer means makes it possible to controlflow time of the reverse current of the means for switching thecurrent-flowing direction.

It is further allowable to provide an absorbancy ratio detector meansinstead of the timer means, which makes it possible to quickly andcorrectly detect the benzenoid/quinoid ratio in the surface polyanilinelayer.

In flowing the current across the heat exchanger and the oppositeelectrode, it is further desirable to control the current relying uponthe amount of current flowing or the amount of electric charge. Forexample, it is recommended to further provide a means for measuring theamount of current flowing or the amount of electric charge to controlthe time for flowing the electric current.

The heat exchanger of the invention can be produced according to variousmanners, and described below is one example.

First, the aluminum material is molded to fabricate heat-exchangingmembers such as tube members, fins and plates. These members are brazedat a high temperature of not lower than 600° C. to produce a precursorfor the heat exchanger in a desired shape. Next, the brazing agent usedfor joining the members is removed by washing the precursor by using anacid or an alkali, and further washed with water followed by drainingthe water off and drying. Drying is conducted, for example, at 140° C.for 15 minutes.

Next, the polyaniline film is formed on the surface of the precursor ofthe heat exchanger. In the step of forming the film, the precursor ofthe heat exchanger is dipped in a solution containing the polyanilinefor about 60 seconds, followed by draining the water off and drying. Thepolyaniline-containing solution used here may have a composition, forexample, as described below:

Polyaniline about 1 to about 5% by weight Binder (carbodiimide about 1to about 20% by weight compound) Solvent (water) about 80 to about 98%by weight

Here, the drying step is conducted, for example, at 140° C. for 15minutes. If drying of the precursor is not sufficient, the polyanilinefilm may peel off in a subsequent step, therefore, it is desirable tomake sure during this step that the precursor has sufficiently dried,and after drying, the polyaniline film is formed having a thickness ofabout 0.5 μm.

It is further desirable to execute a film forming-state evaluation stepto evaluate whether the polyaniline film has completely formed, so thatthe solution used in the subsequent steps will not directly infiltrateinto the heat exchanger. The film forming-evaluation state can beexecuted easily and in a short period of time, for example, by observinga predetermined measuring point by using an optical microscope, taking apicture thereof, converting the picture into a binary form (white:aluminum substrate and pinholes, black: polyaniline) by using pictureprocessing software, and detecting the white portion. After the abovestep, the polyaniline film is removed if it is determined that thepolyaniline film has not been perfectly formed (pinholes have occurred).To prevent pitting due to pinholes, a metal film having anoxidation-reduction potential which is higher than the chromate or thepolyaniline is formed as an underlying film, and thereafter, thepolyaniline film is formed to decrease corrosion.

In a heat exchanger equipped with the tube having fins composed of thealuminum member and the surface polyaniline layer covering the aluminummember, a particular electrode structure is provided to vary thestructure ratio of the polyaniline. The electrode structure isconstituted by, for example, a power source, an anode and a cathodeconnected thereto. The surfaces of the electrodes are coated with amaterial having an oxidation-reduction potential which is higher thanthe polyaniline. Voltage is applied to the electrode structure from thepower source. In the case of the present invention, it is desirable toprovide a mechanism for applying a voltage to the electrode structurebefore and after use, in which voltage is opposite to that of duringuse, and a timer for controlling the time of application to be constant,in order to apply the potential and opposite potential.

According to the present invention, the aim of providing the mechanismfor controlling the applied voltage is to return the polyaniline, ofwhich the structure has changed, back to the structure before beingused, as easily understood from the foregoing description with referenceto FIGS. 9 to 13. As illustrated in FIGS. 11 and 12, the aim is toreturn the benzenoid structure, of which the ratio has increased, backto the quinoid structure. However, if the opposite potential iscontinuously applied for an extended period of time, the quinoidstructure increases to a degree more than expected and other portionsare oxidized, causing the polyaniline to become soluble in water andelute out into water from the electrode plate. It is, therefore,desirable that the application of the opposite potential be measured byusing a timer in order to discontinue the application. Further, a methodfor correctly measuring the time is to measure the absorbancy in thestructure in which light transmits through a part of the electrode. Inthis case, a peak in the quinoid structure is observed near to 650 nm,and a peak in the benzenoid structure is observed near to 350 nm.Thereby, application of the opposite potential may be discontinued bysetting the peak ratio.

EXAMPLES

The invention will be further described with reference to Examplesthereof. However, it should be noted that the invention is in no waylimited to these Examples only.

Fabrication of a Tube with Fins

An aluminum alloy (AlMn alloy) was molded to produce a tube and fins aspartly shown in FIG. 2. The brazing temperature was about 600° C. Afterhaving confirmed the junction between the tube and fins, the brazingagent after use was dissolved with diluted sulfuric acid and removed,followed by washing with water to a sufficient degree. After the waterwas drained off, the obtained precursor was dried at 140° C. for 15minutes.

Next, the polyaniline film was formed on the surface of the precursorafter drying. The polyaniline-containing solution possessed thefollowing composition:

Polyaniline about 1 to about 5% by weight Binder (carbodiimide about 1to about 20% by weight compound) Solvent (water) about 80 to about 98%by weight

Thereafter, the precursor was dipped in the above polyaniline-containingsolution (liquid temperature: about 20° C.) for about 60 seconds,followed by draining and drying. The drying step was conducted, forexample, at 140° C. for 15 minutes. Tubes were obtained with fins coatedon the whole surfaces thereof with a surface polyaniline film having athickness of about 0.5 μm.

Use in the Heat Exchanger

The tube with fins obtained above were used in a car heat exchanger asshown in FIG. 1 to examine performance. As a result, the tube with finsexhibited excellent durability exhibiting functions for decomposingmalodorous substances deposited on the surfaces of the tube and fins,and sterilizing harmful microorganisms. It was further confirmed thatnot only the functions for decomposing and deodorizing malodoroussubstances and sterilizing organic microorganisms could be efficientlyexhibited, but also the ratio of the benzenoid structure to the quinoidstructure could be maintained in the polyaniline to suppress malodorswithout lowering the active oxygen generating capability of thepolyaniline after it was formed and was used, and the basic performanceof the heat exchanger could be maintained.

Testing for Evaluation

The obtained tube with fins was put through the following testing inorder to evaluate the benzenoid/quinoid ratio in the surface polyanilinelayer and a change in the active oxygen generating capability with thepassage of time.

(1) Preparation of Samples

Samples were prepared by attaching an anode and a cathode to the surfacepolyaniline layer of the tube with fins to apply an electric potentialand opposite potential of 2 volts. The anode and cathode wereconstituted by using a titanium based material and a carbon basedmaterial. A power source was provided as a voltage applying means forapplying voltage to these electrodes to flow an electric current.

(2) Application of Electric Potential

The anode of the sample was connected to the power source (+), thesample was dipped in 50 ml of pure water, and thereafter, a voltage of 2volts was applied for different periods of time (0 hour, 24 hours and 96hours) by stirring with a stirrer. The eluates were measured for theirabsorbancy spectra for their respective times by using an absorbancymeter “UV-2500PC” (a trade name) manufactured by Shimazu Mfg. Co., andthe results were plotted as shown in FIG. 9. From these results, it waspresumed that a change in the structure occurred in the polyaniline asshown in FIG. 10.

(3) Application of Opposite Potential

Following the above step, the cathode of the sample was connected to thepower source (+), and the sample was dipped in 50 ml of pure water. Avoltage of 2 volts was applied for different periods of time (0 minute,30 minutes and 60 minutes) by stirring with a stirrer. The eluates weremeasured for their absorbancy spectra for their respective times byusing the absorbancy meter (described above), and the results wereplotted as shown in FIG. 11. From these results, it was presumed that achange in the structure occurred in the polyaniline as shown in FIG. 12.In other words, due to the application of the opposite potential, thequinoid structure increased, and the active oxygen generating capabilitywas restored.

(4) Conclusion

Based on the measured results of FIGS. 9 and 11, the benzenoid/quinoidratios and the active oxygen generating capabilities (ppm) were plottedas a function of time to obtain a graph as shown in FIG. 13. Asunderstood from this graph, the benzenoid/quinoid ratio could berestored to the initial state by applying the opposite potential foronly a short period of time. Accompanying this restoration, the activeoxygen generating capability could also be restored near to the initialstate.

1. A heat exchanger equipped with at least one tube having at least onefin, wherein: said at least one tube and/or said at least one fin beingcomposed of at least a base body and a surface film formed on at least aportion of an uppermost surface of the base body, the surface film is asurface polyaniline layer composed of a polyaniline and/or a derivativethereof capable of generating active oxygen or hydrogen peroxide byreacting with a water component in external air that comes in contacttherewith, and a ratio of benzenoid to quinoid in the surfacepolyaniline layer is in a range of 0.5 to 3.0, which is defined as aratio of an absorbancy of a benzenoid structure to an absorbency of aquinoid structure in the polyaniline and/or in the derivative thereof.2. The heat exchanger according to claim 1, wherein the ratio ofbenzenoid to quinoid is in a range of 1.0 to 2.0.
 3. The heat exchangeraccording to claim 1, wherein the surface polyaniline layer is formed onthe entire uppermost surface of the base body.
 4. The heat exchangeraccording to claim 1, wherein the surface polyaniline layer further hasat least one kind of hydrophilic functional group introduced therein. 5.The heat exchanger according to claim 4, wherein said at least one kindof hydrophilic functional group is selected from the group consisting ofa primary amino group, a secondary amino group, a tertiary amino group,an ammonium group, a nitric acid group, a carboxyl group, a sulfonicacid group and a hydroxyl group.
 6. The heat exchanger according toclaim 4, wherein said at least one kind of hydrophilic functional groupis one that stems from a binder used for forming the surface polyanilinelayer from the polyaniline and/or the derivative thereof.
 7. The heatexchanger according to claim 6, wherein said at least one kind ofhydrophilic functional group is one that has been introduced in thebinder in advance.
 8. The heat exchanger according to claim 1, whereinthe base bodies of said at least one tube and/or said at least one finare the ones which have been formed by molding a metallic material. 9.The heat exchanger according to claim 8, wherein the metallic materialis composed of a metallic material containing aluminum.
 10. The heatexchanger according to claim 1, wherein the base bodies of said at leastone tube and/or said at least one fin are composed of a composite bodyof at least two layers of metallic materials, wherein an amount of ametallic material having a higher oxidation-reduction potentialincreases from an upper metallic material layer toward a lower metallicmaterial layer.
 11. The heat exchanger according to claim 10, whereinthe base bodies of said at least one tube and/or said at least one finare composed of a composite body of two layers of metallic materials,wherein a lower metallic material layer of the composite body iscomposed of an aluminum (Al) alloy, and an upper metallic material layerof the composite body is composed of a zinc (Zn)-containing metallicmaterial.
 12. The heat exchanger according to claim 11, wherein thelower metallic material layer is composed of an Al—Mn based alloy, andthe upper metallic material layer is composed of a metallic materialcontaining silicon (Si) in addition to zinc.
 13. The heat exchangeraccording to claim 12, wherein the upper metallic material is composedof an aluminum alloy containing aluminum (Al) and impurities, inaddition to zinc and silicon.
 14. The heat exchanger according to claim1, wherein the surface polyaniline layer further contains a dopant. 15.The heat exchanger according to claim 14, wherein the dopant is adheredto the polyaniline and/or the derivative thereof due to an electrostaticinteraction.
 16. The heat exchanger according to claim 1, wherein saidat least one tube and/or said at least one fin further have at least oneinterlayered intermediate layer between the base body thereof and thesurface polyaniline layer.
 17. The heat exchanger according to claim 16,wherein said at least one interlayered intermediate layer is composed ofa nonmetallic material.
 18. The heat exchanger according to claim 16,wherein said at least one interlayered intermediate layer is selectedfrom the group consisting of an insulating film, an antioxidizing film,and a film composed of a nonmetallic material having a higheroxidation-reduction potential than that of the polyailine and/or thederivative thereof.
 19. The heat exchanger according to claim 1, furthercomprising structure-converting means for converting the benzenoidstructure constituting the polyaniline and/or the derivative thereofinto the quinoid structure, or for converting the quinoid structure intothe benzenoid structure, in order to bring the ratio of benzenoid toquinoid back into a preset range of 0.5 to 3.0, when the ratio ofbenzenoid to quinoid has fallen outside the preset range in the surfacepolyaniline layer.
 20. The heat exchanger according to claim 19, whereinthe structure-converting means is voltage-applying means, whereinelectrons are removed from the surface polyaniline layer, by arrangingan opposite electrode composed of another substrate to the heatexchanger, and flowing a current between the heat exchanger and theopposite electrode via the voltage-applying means.
 21. The heatexchanger according to claim 20, wherein the structure-converting meansis the voltage applying means with a means for changing the direction ofcurrent, and a current is flowed between the heat exchanger and theopposite electrode by reversing the direction of current, when the ratioof benzenoid to quinoid has become greater than the preset range of 0.5to 3.0.
 22. The heat exchanger according to claim 19, further comprisingtimer means for controlling a time period in which the current isreversely flowed by the means for changing the direction of current. 23.The heat exchanger according to claim 19, further comprisingabsorbancy-ratio detecting means for detecting the ratio of benzenoid toquinoid in the surface polyaniline layer.
 24. The heat exchangeraccording to claim 20, wherein when a current is flowed between the heatexchanger and the opposite electrode, the flow of current is controlleddepending upon an amount of electric current that flows or upon anamount of electric charge.
 25. The heat exchanger according to claim 20,further comprising means for measuring the amount of current flow or theamount of electric charge thereby to control the time period for flowingthe electric current.
 26. The heat exchanger according to claim 1,wherein the surface polyaniline layer is further formed also on theuppermost surface of said at least one tube.
 27. The heat exchangeraccording to claim 1, which is used for a vehicle air conditioner.